1. Field of the Invention
The present invention relates to a high quality transmission projection screen for use with a transmitting type (rear-view) projection television.
2. Description of the Prior Art
It is essential for a transmission projection screen employed as the viewing screen of a rear-projection television to have a wider viewing angle and provide a projected image of high resolution and brightness. Such a transmission projection screen has a substrate containing a mixture of light diffusing medium for rendering the projected light visible. The transmission projection screen also incorporates a lenticular lens(es) provided on the surface thereof for anisotropic diffusion of the projected light while enhancing the luminance of an image throughout the viewing angle. Additionally, a Fresnel lens which serves as a field lens to the flux of projected light, is used in combination with the projection screen for minimizing decline in the luminance at the edge region of the projection screen.
For enhancement of the resolution of the transmission projection screen, it is practical to have the substrate section of the same, which contains the light diffusing medium for rendering the projected light visible, reduced in the thickness and allow the lenticular lens provided on the surface to reduce in the lens pitch. A method of thinning the substrate section containing light diffusing medium is disclosed in Japanese Patent Laid-open Publication No. 63-273850 (1988) in which a thin film of substrate is formed from a mixture of light diffusing medium and resin and attached to the surface of a transmission projection screen. However, it is still difficult in practice to have a lenticular lens of narrower lens pitch adapted for anisotropic diffusion of the projected light to provide high resolution. For example, it becomes remarkably intricate to fabricate forming molds of providing a lenticular lens on the surface of the transmission projection screen. Also, the useable life of such complex forming molds is hardly extended in the relation to forming shots, which causes the overall cost to increase.
A known transmitting type projection television is generally arranged in which an image developed on the phosphor screen of a cathode ray tube is projected through a projection lens onto a large-size transmission projection screen. It is also known that liquid crystal panels are used as light valves to constitute a projector in a transmitting type projection television. More particularly, when patterns of image information are developed on the liquid crystal panels by means of variation in the transmittance according to image signals, the light incident on the back of the liquid crystal panels is modulated to produce a visual image on the transmission projection screen through projection by a projection lens. In this method, each of the liquid crystal panels comprises a plurality of very small light valve elements provided in a matrix arrangement and thus, an image projected through the projection lens onto the transmission projection screen is constituted by a corresponding matrix form of pixels. The interaction between the pixel matrix and the lenticular lens of the transmission projection screen will cause Moire effects, thus lowering picture quality. It is also necessary for visual effect that the pitch of the lenticular lens of the transmission projection screen is considerably narrowed so as to ensure no decline in the picture quality. Similarly as described previously, it becomes troublesome to fabricate forming molds of providing such a narrow-pitch lenticular lens on the surface of the transmission projection screen. Also, the life of the forming molds cannot be kept long as the number of forming shots increases. As a result, the production cost will rise.